The operation of airlines and airports today focuses on achieving maximum efficiency to keep operating costs as low as possible while continuing to provide travelers with a safe and economical mode of travel. It is desired to keep the time an aircraft spends on the ground at an airport between arrival at and departure from the gate to the minimum required to unload arriving passengers and cargo, service the aircraft, and load departing passengers and cargo. Minimizing this turnaround time not only reduces delays in airline flight schedules, but also increases the possibility that an airline can schedule additional flights, providing travelers with more options and improving airline profits. Increased aircraft ground traffic, however, may be accompanied by an increased risk of ground incidents involving aircraft, ground vehicles, and even passengers and ground personnel. Consequently, reducing aircraft turnaround time should not be at the expense of increased ground safety risks.
The ramp area of an airport typically includes the jetway or airbridge and the ground area around where aircraft park between arrival and departure adjacent to the terminal. The ramp entry or exit area, which is the area adjacent to a taxiway and leading to or from an airline's ramp is, according to some studies, the location of most ground incidents. At this location, taxi lines leading into and out of the gate area converge, and an aircraft is less likely to be in communication with air traffic or other controllers. Flight crew are more likely at this point to be relying on an airline's ramp control procedure or ground crew input for guidance. The largest percentage of incidents in one study occurred within 20 feet of the nose wheel parking line, within the gate stop area, when the flight crew is typically relying entirely on ground crew guidance and signals from ground crew or elsewhere for clearance from obstacles and for final taxi instructions. Increased ramp congestion may be exacerbated by inadequate numbers of ground personnel, leading to the likelihood of increased ramp incidents.
One study found that more incidents occur during aircraft arrival than during departure. One possible explanation for this is that there may be more obstacles for an aircraft to encounter when entering the congested area next to gates and terminal buildings. Another reason may be related to the large number of pushback, power-out, and power-turn procedures that are conducted during departure operations while arriving aircraft are entering the ramp area.
While damage caused by aircraft to ground equipment and service vehicles may account for most of the reported ramp incidents, damage to other aircraft, especially where taxiing aircraft share a common maneuvering area, and injuries to people, mainly ground personnel but occasionally passengers, can account for a significant number of additional incidents. The personal injuries notwithstanding, the financial and other losses to an airline from such incidents are potentially substantial.
In addition to ramp collision incidents such as those described above, ramp safety, and ground safety generally, can be significantly compromised by the jet blast from an aircraft jet engine, as well as by the potential for engine ingestion when aircraft engines are kept in operation, even at idle speeds, within the ramp area. Ramp congestion caused by increasing numbers of flights, stringent aircraft scheduling requirements, and efforts to squeeze large jets into gates originally designed for much smaller aircraft contributes to traffic jams and reduced maneuvering space in the ramp area. The addition of jet blast, also known as jet efflux, from aircraft taxiing into a congested ramp area with one or more engines operating virtually guarantees that something will be damaged or someone will be injured.
Jet blast data, measured from the tail with the engines at low RPM settings, indicates that the damage profile can extend from the outboard wing-mounted engines to more than 200 feet beyond some larger aircraft. Within this area, jet engines can generate hurricane-level exhaust forces of almost 100 knots. Most of the reported jet blast damage incidents typically occur in the ramp area during pushback, power back, taxi-out, or taxi-in. The position of the operating jet engines relative to gates, ground equipment, people, and other aircraft, especially smaller light aircraft, can significantly influence the occurrence of jet blast damage incidents when breakaway power is applied. Aircraft with engines powered and in the process of turning are frequently involved in jet blast damage incidents. Using powered engines to maneuver an aircraft without assistance from a tractor or tug is highly likely to compromise ramp and ground safety. The presence of a tractor or tug, however, is not likely to prevent jet blast damage if the aircraft's engines are running and the aircraft is in the process of making a sharp turn. Careful management of an engine-powered aircraft moving on the ground is required to prevent jet blast damage, particularly on congested ramps not designed for large aircraft.
Positioning a jet aircraft so that the forward thrust is directed away from gate areas, people, and ramp equipment and the jet blast is not directed into the gate area is helpful, but the direction of the jet blast can change as the aircraft is maneuvered into or out of the gate. This occurs, for example, during power back operations, when the flight crew employs engine thrust reversers to direct thrust ahead of the aircraft to push the aircraft backward, changing the direction of the jet blast. Damage to other aircraft, especially small aircraft, ground vehicles, and personnel remains a distinct possibility as long as an aircraft's engines are running.
Suggestions for preventing jet blast damage thus far have been limited to, for example, avoiding sharp turns on taxi-in or pushback with one or more engines running, and using tractors or tugs to move taxiing aircraft. Improving ground crew vigilance, communication, and the handling of ground vehicles, as well as parking small commuter aircraft in locations away from jet aircraft have also been recommended. These suggestions may reduce damage from jet blast. As long as jet aircraft continue to operate their engines while the aircraft are on the ground, however, jet blast continues to be a hazard.
Another hazard posed by aircraft engines operating in the ramp area, especially at or near the gate, is the potential that engine ingestion could occur. The operation of a jet engine creates a low pressure area in the engine inlet, which causes a large quantity of air from the area forward of the inlet cowl to move into the engine. The velocity of the air nearest the inlet is much greater than the velocity of the air farther from the inlet. As a result, the amount of engine suction close to the inlet is significant and may be high enough to pull tools, equipment, and even people into the engine. To avoid the possibility of serious injury or, in rare cases, death, it is necessary for ground personnel and ground vehicles to keep a safe distance from an operating aircraft engine. The hazard or danger zone around one type of aircraft with an engine operating just above idle power is within a radius of about 9 feet (2.7 m) from the center of the engine and about 4 feet (1.2 m) back toward the engine cowl. This hazard zone increases to a radius of about 13 feet (4 m) and a distance toward the cowl of about 5 feet (1.5 m) when the aircraft engine is operating above idle power. At higher power levels, the hazard zone increases to at least 100 feet (m) in front of the engines and at least 200 feet (m) behind the engines. The extent of the engine ingestion hazard zone may be increased by wind or weather conditions. Where the engine ingestion hazard zone ends in the vicinity of the engine cowl, the exhaust hazard area begins, and damage or injury from jet blast hazard is possible. The danger of aircraft turbines, whether they are pure jet engines or turboprop engines, cannot be overstated.
Even after the aircraft engine is shut off completely, the possibility of engine ingestion may exist for a period of about 30 seconds. The risk of engine ingestion to a person standing in front of an engine the size of a 737 NG engine that has just been turned off is extremely high. Hazard warning stripes and other indicia are typically painted on the engine cowl to warn ground personnel of the potential danger. Some airline operators have painted engine inlet hazard zones on the tarmac at aircraft parking locations. This will be effective only if the aircraft is parked accurately within the hazard zone. Crowded conditions in ramp gate areas further increase the possibility for engine ingestion damage or injury. Engine ingestion damage or injury at or near an airport gate area can be completely avoided only when the aircraft engines are shut down and remain off.
A system and method for reducing turnaround time of an aircraft is described in U.S. Patent Application Publication No. US 2008/0059053 (now U.S. Pat. No. 7,891,609) to Cox et al, owned in common with the present application. The system and method described therein suggests that aircraft turbines may be turned on only when needed for takeoff or prior to landing and are turned off until takeoff or after landing. The aircraft is moved along taxiways using at least one self propelled undercarriage wheel. This method focuses on reducing turnaround times by having all of the required equipment available for turnaround and departure and minimizing the use of motorized tugs while providing an enhanced communication system between the pilot and ground personnel. A method for reducing aircraft turnaround time by improving ramp safety is not specifically suggested, however.
McCoskey et al also describes a powered nose aircraft wheel system useful in a method of taxiing an aircraft that can minimize the assistance needed from tugs and the aircraft engines in U.S. Pat. No. 7,445,178. A precision guidance system is disclosed for controlling movement of the aircraft on the ground to minimize collision damage during taxi. Reducing aircraft turnaround time by enhancing ramp safety is not suggested.
The prior art, therefore, has not directly recognized a connection between improved ramp safety and reduced aircraft turnaround times and does not disclose a method for simultaneously reducing aircraft turnaround time by improving ramp safety.